Full-duplex signaling for arc event protection

ABSTRACT

In a power protection and distribution assembly a trip system monitors electrical current and sends a current status signal to an arc flash protection system indicating whether current characteristic of an arc event is detected. The arc flash protection system evaluates this current status signal along with a light status signal indicating whether light characteristic of an arc event has been detected. Based on this evaluation, the arc flash protection system sends a control signal to the trip system for controlling the trip system to trip a breaker. The systems each include a full-duplex signaling module for sending the signals between the systems over a pair of conductors. Each signaling module sends one of the signals by modulating the magnitude of a current through or a voltage across the conductors, and receives the other signal by demodulating the magnitude of the current through or the voltage across the conductors, as distinctively modulated by the other signaling module.

FIELD OF INVENTION

The present invention generally relates to arc event protection, andparticularly relates to full-duplex signaling between a trip system andan arc flash protection system.

BACKGROUND

A power protection and distribution assembly is typically installed atevery building, factory, or similar facility, where the main electricalpower from the grid enters the facility. The power protection anddistribution assembly, sometimes referred to as “switchgear,” usuallyincludes an enclosure with a main circuit breaker at the electricalpoint furthest upstream, or closest to the external main power grid; apower distribution bus, which may comprise copper bars for each positivepower phase and one or more ground bus bars; and one or more areacircuit breakers, each protecting an electrical circuit distributingpower to an area of the facility. The purpose of the circuit breakers isto protect downstream circuits from overcurrent conditions, such aswould occur in the event of a short circuit.

A trip system trips a circuit breaker upon the detection of anovercurrent condition. One type of trip system detects an overcurrentcondition by detecting excessive heat generated by large currents movingthrough resistive conductors. While such trip systems will interrupt afaulty circuit in time to avoid a fire, sensitive downstream electricalequipment may still be damaged by the overcurrent condition prior tocurrent flow interruption.

Other functions of trip systems can provide a quicker circuitinterruption operation of the main breaker prior to or during dangerousarcing events through interaction with an arc flash protection system.An arc event, i.e. current traveling through air, manifests itselfvisibly in the form of a spark, arc, flame, glow of molten metal, etc.that results from an arcing condition. When the arc flash protectionsystem detects such an arc event, the system may operate an auxiliaryarc diverter mechanism or send a control signal to the trip systemdirecting the trip system to trip the main circuit breaker, or both.

The arc flash protection system detects an arc event when optical orother conditions characteristic of a flash are detected. The arc flashprotection system detects light as one of these conditions. The tripsystem detects abnormal current flowing through the conductors asanother one of the arcing conditions, and signals the condition to thearc flash protection system.

With signaling between the trip system and the arc flash protectionsystem occurring within the electrical enclosure to prevent damage fromarc flash occurrences, the ability of the systems to communicate statusinformation, and therefore provide timely and accurate circuitinterruption, depends on the speed and robustness of the signaling.Providing high speed and highly robust signaling, without meaningfullyincreasing the complexity and/or cost of the systems, or reducing same;has heretofore proven problematic.

The Background section of this document is provided to place embodimentsof the present invention in technological and operational context, toassist those of skill in the art in understanding their scope andutility. Unless explicitly identified as such, no statement herein isadmitted to be prior art merely by its inclusion in the Backgroundsection.

SUMMARY

Due to the electromagnetic, spacing, and wiring constraints of anenclosed electrical distribution environment, it is desirable to providerobust signaling capabilities in order to maximize the efficiency andfunctionality for arc event protection in a power protection anddistribution assembly. The present invention addresses these concernswith a full-duplex signaling arrangement between constituent trip andarc flash protection systems of the power protection and distributionassembly.

The following presents a simplified summary of the disclosure in orderto provide a basic understanding to those of skill in the art. Thissummary is not an extensive overview of the disclosure. Nor is thesummary intended to identify key/critical elements of embodiments of theinvention or otherwise delineate the scope of the invention. The solepurpose of this summary is to present some concepts disclosed herein ina simplified form as a prelude to the more detailed description that ispresented later.

One or more embodiments herein provide high speed and highly robustfull-duplex signaling between a trip system and an arc flash protectionsystem, without meaningfully increasing the complexity and cost of thosesystems. This high-speed, robust signaling facilitates timely andaccurate tripping of an upstream circuit breaker to protect downstreamcircuits from damage.

More particularly, a trip system herein is configured to send a currentstatus signal to an arc flash protection system indicating whethercurrent characteristic of an arc event has been detected. The arc flashprotection system evaluates this current status signal along with alight status signal indicating whether light characteristic of an arcevent has been detected as well. Based on this evaluation, the arc flashprotection system is configured to send a control signal to the tripsystem for controlling the trip system to trip the upstream breaker andthereby protect downstream circuits from damage.

The trip system and the arc flash protection system each include afull-duplex signaling module for simultaneously signaling the currentstatus signal and the control signal between the systems over a pair ofconductors coupling the systems together. Notably, each signaling modulesends one of the signals by modulating the magnitude of a currentthrough or a voltage across the pair of conductors, and receives theother signal by demodulating the magnitude of the current through or thevoltage across the pair of conductors, as distinctively modulated by theother signaling module.

In some embodiments, for example, one of the signaling modules modulatesthe magnitude of the current through the pair of conductors, while theother one of the signaling modules modulates the magnitude of thevoltage across the pair of conductors. In this case, the signalingbetween the modules is asymmetric in the sense that the modules do notmodulate the same physical property. In other “symmetric” embodiments,by contrast, the signaling modules both modulate either the currentthrough the pair of conductors or the voltage across the pair ofconductors, but the modules do so in ways that are distinguishable.

Some asymmetric embodiments advantageously decouple voltage magnitudemodulation by one of the signaling modules and current magnitudemodulation by the other signaling module. In one embodiment, forexample, the signaling module performing current magnitude modulationdoes so using an adjustable impedance circuit. Notably, this adjustableimpedance circuit is configured to automatically self-adjust itsimpedance in order to substantially counteract any current magnitudemodulation attributable to voltage magnitude modulation performed by theother signaling module. This means that signaling of the current statussignal and signaling of the control signal remain substantiallyindependent without having to introduce significant noise tolerancemargins.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. However, this invention shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

FIG. 1 is a block diagram of a power protection and distributionassembly configured according to one or more embodiments.

FIG. 2A is a block diagram of a trip system and arc flash protectionsystem configured according to one or more asymmetric embodimentsherein.

FIG. 2B is a schematic diagram illustrating one implementation of theasymmetric embodiment shown in FIG. 2A.

FIG. 2C is a schematic diagram of an adjustable impedance circuit shownin FIG. 2B, according to one or more embodiments.

FIG. 2D is a schematic diagram illustrating a different implementationof the asymmetric embodiment shown in FIG. 2A.

FIG. 3A is a block diagram of a trip system and arc flash protectionsystem configured according to one or more symmetric embodiments herein.

FIG. 3B is a schematic diagram illustrating one implementation of thesymmetric embodiment shown in FIG. 3A.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed systems and/or methods may be implementedusing any number of techniques, whether currently known or in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, includingthe exemplary designs and implementations illustrated and describedherein, but may be modified within the scope of the appended claimsalong with their full scope of equivalents.

FIG. 1 depicts an exemplary power protection and distribution assembly10 for a facility. Electrical power from a power source 12 is receivedby switchgear 14, which houses a main circuit breaker 16, powerdistribution bus 18, and one or more area circuit breakers 20A, 20B, . .. 20N. The main breaker 16 protects the entire facility, and is rated topass the highest anticipated sustained current. The power distributionbus 18 may comprise solid copper bars capable of conducting largecurrents. Each area circuit breaker 20A, 20B, . . . 20N downstream fromthe main circuit breaker 16 is rated for a lower current, anddistributes power to separate downstream circuits 22A, 22B, . . . 22N.Separate downstream circuits 22A, 22B, . . . 22N typically distributeelectrical power to separate areas of the facility.

When the power distribution bus 18 (or one of its component parts)experiences a short circuit or an arc flash event, the main circuitbreaker 16 may experience current flow in excess of its rated capacity.This is referred to as an overcurrent condition. The switchgear 14includes a trip system 24 and an arc flash protection system 26 that arecooperatively configured to trip the main circuit breaker 16 when anovercurrent condition occurs, such as during the detection of an arcevent. Tripping the main circuit breaker 16 in this way isolates thepower distribution bus 18 from the power source 12 in a timely manner,before the power distribution bus 18 is damaged. The timeliness andaccuracy of the breaker's tripping, though, depends on the speed androbustness of signaling between the trip system 24 and the arc flashprotection system 26. One or more embodiments herein advantageouslyprovide high speed and highly robust signaling, and thus timely andaccurate breaker tripping, without meaningfully increasing thecomplexity and/or cost of the system 10.

In this regard, a status circuit 28 included in the trip system 24 isconfigured to generate a current status signal 30 indicating whether ornot current characteristic of an arc event is detected. In someembodiments, for example, the status circuit 28 receives the output 32of a current sensor 34 disposed in series with the main breaker 16. Inthis case, the status circuit 28 compares the sensor output 32 to acurrent level threshold that has been set to distinguish between acurrent level that is attributable to an arc event and a current levelthat is not. When the sensor output 32 indicates a current level thatmeets or exceeds the arcing threshold, the status circuit 28 generatesthe current status signal 30 to indicate that a current characteristicof an arc event has been detected. Otherwise, the status circuit 28generates the current status signal 30 to indicate that such a currenthas not been detected.

The trip system 24 further includes a signaling module 36 that isconfigured to send the current status signal 30 to the arc flashprotection system 26. The signaling module 36 is full-duplex in thesense that the module 36 can send the current status signal 30 to thearc flash protection system 26 while simultaneously receiving signalingfrom the arc flash protection system 26. Regardless, the signalingmodule 36 sends the current status signal 30 to the arc flash protectionsystem 26 by modulating the magnitude of a current through or a voltageacross a pair of conductors 38 coupling the trip system 24 to the arcflash protection system 26. The arc flash protection system 26correspondingly includes a full-duplex signaling module 40 configured toreceive the current status signal 30′ from the trip system 24 bydemodulating the magnitude of the current through or the voltage acrossthe pair of conductors 38.

In addition to obtaining the current status signal 30′ indicatingwhether or not current characteristic of an arc event is detected, thearc flash protection system 26 obtains a light status signal 42indicating whether or not light characteristic of an arc event isdetected. In at least some embodiments, the arc flash protection system26 obtains this light status signal 42 by generating it based on theoutput 46 of one or more light sensors 48 disposed within the switchgear14, e.g., proximal to the one or more area circuit breakers 20. In onesuch embodiment, for example, the arch flash protection system 26includes a status circuit 44 configured to compare the sensor output 46to a light level threshold that has been set to distinguish between alight level that is attributable to an arc event and a light level thatis not. When the sensor output 46 indicates a light level that meets orexceeds the threshold, the status circuit 44 generates the light statussignal 42 to indicate that light characteristic of an arc event has beendetected. Otherwise, the status circuit 44 generates the light statussignal 42 to indicate that such light has not been detected.

Based on the current status signal 30′ received from the trip system 24and the light status signal 42 generated by the status circuit 44, acontroller 50 included in the arc flash protection system 26 generates acontrol signal 52 for controlling the trip system 24 to trip the maincircuit breaker 16. In one embodiment, for example, the controller 50generates the control signal 52 to direct the trip system 24 to trip themain breaker 16, responsive to the light status signal 42 and thecurrent status signal 30′ indicating that both light and currentcharacteristic of an arc event have been detected. Otherwise, if eitherlight or current characteristic of an arc event has not been detected,the controller 50 generates the control signal 52 to direct the tripsystem 24 to maintain its current state, i.e. no trip signal isgenerated.

Regardless, the arc flash protection system's full-duplex signalingmodule 40 sends this control signal 52 to the trip system 24 bymodulating the magnitude of the current through or the voltage acrossthe pair of conductors 38. Modulation performed by the arc flashprotection system's full-duplex signaling module 40 in this regard isdistinctive from the modulation performed by the trip system'sfull-duplex signaling module 36. In some embodiments, for example, oneof the signaling modules 36, 40 modulates the magnitude of the currentthrough the pair of conductors 38, while the other one of the signalingmodules 36, 40 modulates the magnitude of the voltage across the pair ofconductors 38. In this case, the signaling between the modules 36, 40 isasymmetric in the sense that the modules 36, 40 do not modulate the samephysical property. In other “symmetric” embodiments, by contrast, thesignaling modules 36, 40 both modulate either the current through thepair of conductors 38 or the voltage across the pair of conductors 38,but the modules 36, 40 do so in ways that are distinguishable.

With the arc flash protection system's signaling module 40 sending thecontrol signal 52 by distinctively modulating the current through or thevoltage across the pair of conductors 38, the trip system's signalingmodule 36 correspondingly receives the control signal 52′ bydemodulating that current or voltage. A driver 54 included in the tripsystem 24 is configured to trip the main breaker 16 in accordance withthis control signal 52′. That is, the driver 54 either signals the mainbreaker 16 to trip or maintain the current state of the main breaker 16depending on the command indicated by the control signal 52′.

FIGS. 2A-2D illustrate additional details according to one or moreasymmetric embodiments. As shown in FIG. 2A, the trip system's signalingmodule 36 includes a transmitter 56 in series with a receiver 58 betweenthe conductors 38. The arc flash protection system's signaling module40, by contrast, includes a transmitter 60 in parallel with a receiver62 (and the conductors 38). The trip system's transmitter 56 sends thecurrent status signal 30 by modulating the magnitude of the voltageacross the conductors 38, while the trip system's receiver 58 receivesthe control signal 52′ by demodulating the magnitude of the currentthrough the conductors 38 (which is the same as the current through thetrip system's transmitter 56). Correspondingly, the arc flash protectionsystem's transmitter 60 sends the control signal 52 by modulating themagnitude of the current through the conductors 38, while the arc flashprotection system's receiver 62 receives the current status signal 30′by demodulating the magnitude of the voltage across the conductors 38.

In some embodiments, demodulating the magnitude of the voltage acrossthe conductors 38 entails the arc flash protection system's receiver 62monitoring the full voltage across the conductors 38. As shown in FIG.2A, for instance, the full voltage across the conductors 38 falls acrossthe transmitter 60 and the receiver 62 monitors this full voltage. Inother embodiments, though, demodulating the magnitude of the voltageacross the conductors 38 entails the receiver 62 monitoring only a partof that full voltage. For example, where the full voltage across theconductors 38 is divided between the transmitter 60 and one or moreother components (not shown) in series with the transmitter 60,demodulation may entail monitoring the voltage across one or more ofthose other components, or monitoring the voltage across the transmitter60.

FIG. 2B illustrates one implementation of the asymmetric embodimentshown in FIG. 2A. In FIG. 2B, the trip system's transmitter 56 includesan adjustable voltage source 64. The transmitter 56 in this case isconfigured to modulate the magnitude of the voltage across theconductors 38 by adjusting the voltage output of the adjustable voltagesource 64, responsive to the current status signal 30. The arc flashprotection system's receiver 62 correspondingly includes a voltagesensor 66 (e.g., an analog isolator) configured to monitor the magnitudeof the voltage across the conductors 38 for demodulation.

Also in FIG. 2B, the arc flash protection system's transmitter 60includes an adjustable impedance circuit 68. The transmitter 60 in thiscase is configured to modulate the magnitude of the current through theconductors 38 by adjusting the impedance of the adjustable impedancecircuit 68. The trip system's receiver 58 correspondingly includes acurrent sensor 70 configured to monitor the magnitude of this currentfor demodulation. As shown, the current sensor 70 comprises anoperational amplifier 74 connected across a sensing element 72 such as asmall shunt resistor.

In at least some embodiments, the adjustable impedance circuit 68 inFIG. 2B comprises a switchable impedance that is configured toselectively connect different fixed-valued impedances across theconductors 38, responsive to the control signal 52. In otherembodiments, the adjustable impedance circuit 68 comprises acontrollable impedance that is configured to vary in impedanceresponsive to the control signal 52.

Regardless of the particular implementation of the adjustable impedancecircuit 68, the signaling modules 36, 40 in one or more embodiments areconfigured to tolerate at least some coupling between voltage magnitudemodulation by the adjustable voltage source 64 and current magnitudemodulation by the adjustable impedance circuit 68. In this case, whenthe adjustable voltage source 64 changes the magnitude of the voltageacross the conductors 38 in order to send the current status signal 30,the magnitude of the current through the conductors 38 changes as well.Appropriate noise margins at the receiver 58, though, permit thereceiver 58 to distinguish between current magnitude modulationattributable to the adjustable impedance circuit 68 sending the controlsignal 52 and current magnitude modulation incidentally attributable tothe adjustable voltage source 64 sending the current status signal 30.

FIG. 2C illustrates more sophisticated embodiments that substantiallydecouple voltage magnitude modulation by the adjustable voltage source64 and current magnitude modulation by the adjustable impedance circuit68. As shown in FIG. 2C, the arc flash protection system's transmitter60 includes an adjustable impedance circuit 68 that is configured toautomatically self-adjust its impedance in order to substantiallycounteract any modulation of the magnitude of the current through theconductors 38 attributable to modulation by the trip system 24 of themagnitude of the voltage across the conductors 38.

In particular, the adjustable impedance circuit 68 in FIG. 2C isconfigured to self-adjust its impedance as needed in order to regulateor otherwise maintain the current through the conductors 38 at amagnitude representative of the control signal 52. The circuit 68 inthis regard includes a current sensor 78 (similar to current sensor 70)that is configured to monitor the magnitude of the current through theconductors 38. The circuit 68 also includes an impedance controller 76that is configured to determine the difference between the currentmagnitude representative of the control signal 52 (e.g., via isolator75) and the current magnitude through the conductors 38, as monitored bythe current sensor 78. The impedance controller 76 controls anadjustable impedance 80 included in the circuit 68, as needed, tominimize this determined difference.

For example, when the trip system's transmitter 56 of FIG. 2B changesthe magnitude of the voltage across the conductors 38 in order to sendthe current status signal 30, the impedance controller 76 of FIG. 2Cobserves this voltage magnitude change as a corresponding currentmagnitude change and controls the adjustable impedance 80 to counteractthat change. Specifically, when the trip system's transmitter 56 of FIG.2B increases the voltage magnitude across the conductors 38, the currentmagnitude through the conductors 38 increases above the currentmagnitude representative of the control signal 52. The impedancecontroller 76 responsively increases the impedance of the adjustableimpedance 80 so that the current magnitude through the conductors 38decreases back down to the current magnitude representative of thecontrol signal 52. The impedance controller 76 conversely decreases theimpedance of the adjustable impedance 80 responsive to the trip system'stransmitter 56 decreasing the voltage magnitude across the conductors38, so that the current magnitude through the conductors 38 increasesback up to the current magnitude representative of the control signal52. With voltage and current magnitude modulation advantageouslydecoupled in this way, voltage magnitude changes do not producecorresponding current magnitude changes. This means that signaling ofthe current status signal 30 and signaling of the control signal 52remain substantially independent without having to introduce significantnoise tolerance margins, especially when galvanic isolation is employedat one of the signaling modules 36, 40.

Consider a simple example where the signaling modules 36, 40 send thecurrent status signal 30 and the control signal 52 by employing unipolarmodulation between different discrete voltage and current magnitudes. Inthis case, the trip system's transmitter 56 is configured to set thevoltage output of the adjustable voltage source 64 to a first voltagemagnitude (e.g., 5V) in order to send a binary 0 as the current statussignal 30 (e.g., indicating that current characteristic of an arc eventhas not been detected). The arc flash protection system's voltage sensor66 senses the resulting voltage across the conductors 38. When thissensed voltage is within a first predefined voltage magnitude range(e.g., 4-6V), the controller 50 of FIG. 2B recognizes the sensed voltageas a binary 0 sent from the trip system's status circuit 30. Meanwhile,the arc flash protection system's adjustable impedance circuit 68 isconfigured to regulate the current through the conductors 38 to a firstcurrent magnitude (e.g., 4ma) in order to simultaneously send a binary 0as the control signal 52 (e.g., indicating that the driver 54 is tomaintain the current state of the main breaker 16). The trip system'scurrent sensor 70 senses the resulting current through the conductors38. When this sensed current falls within a first predefined currentmagnitude range (e.g., 3-5ma), the driver 54 recognizes the sensedcurrent as a binary 0 sent from the controller 50.

Referring to FIG. 2B, at some point thereafter, the trip system's statuscircuit 28 switches from generating the current status signal 30 toindicate that current characteristic of an arc event has not beendetected, to generating the current status signal 30 to indicate thatsuch a current has been detected. The trip system's transmitter 56correspondingly sets the voltage output of the adjustable voltage source64 to a second voltage magnitude (e.g., 8V) in order to send a binary 1as the current status signal 30. The arc flash protection system'svoltage sensor 66 senses the resulting voltage across the conductors 38.If this sensed voltage falls within a second predefined voltagemagnitude range (e.g., >7V, to provide a noise margin between 6-7V), thecontroller 50 recognizes the sensed voltage as a binary 1 sent from thetrip system's status circuit 30. Meanwhile, the arc flash protectionsystem's adjustable impedance circuit 68 automatically self-adjusts itsimpedance in order to maintain the current through the conductors 38 atthe first current magnitude (e.g., 4ma), despite the change in thevoltage magnitude across the conductors 38. This way, the trip system'scurrent sensor 70 continues to sense current within the first predefinedcurrent magnitude range, and the driver 54 continues to recognize thesensed current as a binary 0 sent from the controller 50 so as tomaintain the current state of the main breaker 16 unless directed to doso by the controller 50.

That said, if the light status signal 42 indicates that lightcharacteristic of an arc event is detected as well, then the controller50 generates the control signal 52 to indicate that the driver 54 is tosignal a trip of the main breaker 16. The arc flash protection system'sadjustable impedance circuit 68 correspondingly adjusts in impedance(e.g., decreases) so that the current through the conductors 38 changesfrom the first current magnitude (e.g., 4ma) to a second currentmagnitude (e.g., 10ma) associated with a binary 1. The trip system'scurrent sensor 70 senses this change in current through the conductors38. If the resulting current falls within a second predefined currentmagnitude range (e.g., >8ma, to provide a noise margin between 5-8ma),the driver 54 recognizes the sensed current as a binary 1 sent from thecontroller 50. The driver 54 then trips the main breaker 16.

As a practical matter, though, the driver 54 in some embodiments isconfigured to selectively ignore (blank) the current output of the tripsystem's receiver 58 for a predefined duration after a state change ofthe current status signal 30′. This way, the driver 54 tolerates theamount of time needed in practice for the arc flash protection system'sadjustable impedance circuit 68 to respond to the voltage magnitudemodulation associated with that state change. The predefined duration inone or more embodiments therefore corresponds to the longest expectedsettling time of the adjustable impedance circuit 68. This duration maybe kept small by judicious adjustment of response times. The sameselective ignoring may similarly extend to the arc flash protectionsystem's controller 50, in order to tolerate the settling time of theadjustable voltage source 64.

Note, too, that the embodiments just described prove particularlyconvenient for supervising the integrity of the signaling path providedby the conductors 38 between the modules 36, 40. In some embodiments,for example, the arc flash protection system's controller 50 or anintegrity monitoring circuit (not shown) included in the arc flashprotection system's receiver 62 monitors for whether the voltage acrossthe conductors 38 falls within a third predefined voltage magnituderange (e.g., 0-3V, to provide noise margin between 3-4V). If the voltagefalls within this range, the integrity of the signaling path has beencompromised and a signaling path error is declared. Additionally oralternatively, the trip system's driver 54 or an integrity monitoringcircuit (not shown) included in the trip system's receiver 58 monitorsfor whether the current through the conductors 38 falls within a thirdpredefined current magnitude range (e.g., 0-2ma, to provide noise marginbetween 2-3ma). If the current falls within this range, the integrity ofthe signaling path has been compromised and a signaling path error isdeclared.

While the above embodiments described the signaling modules 36, 40 asemploying unipolar magnitude modulation, the modules 36, 40 may beconfigured in other embodiments for bipolar magnitude modulation.Further, although the above embodiments employed certain separationbands or noise margins between different discrete levels representativeof different magnitude modulation states, these separation bands may bearbitrarily adjusted to achieve optimal noise immunity. Still further,although the current status signal 30 and the control signal 52 weredescribed above as being represented by a single change in state of thevoltage or current magnitude, the signals 30, 52 in other embodimentsmay be represented by a train of state changes. Moreover, although thesignaling modules 36, 40 were described above as using modulationbetween different discrete voltage and current magnitudes, the modules36, 40 in other embodiments use modulation between different continuousvoltage and current magnitudes. The rapidity of such modulation islimited only by the response times of the transmitters 56, 60, theresponse times of the receivers 58, 62, and the transmissioncharacteristics of the conductors 38.

Contrasted with FIG. 2B, FIG. 2D illustrates a different implementationof the asymmetric embodiment shown in FIG. 2A. Rather than the tripsystem's transmitter 56 including an adjustable voltage source 64, thetransmitter 56 comprises an impedance circuit 82. The transmitter 56 isconfigured to modulate the magnitude of the voltage across theconductors 38 by adjusting the impedance of the impedance circuit 82,responsive to the current status signal 30. As shown, for example, theimpedance circuit 82 includes switched impedance element 84 that is inseries with a fixed voltage source 86. FIG. 2D is otherwise the same asFIG. 2B.

The asymmetric embodiments discussed above prove advantageous inachieving highly robust full-duplex signaling. For example, theasymmetric embodiments achieve high overall noise immunity by permittingthe separation bands of logic high and low signal levels to bearbitrarily adjusted. In at least some contexts, though, the asymmetricembodiments prove more complex in terms of their hardware requirementsand backwards compatibility than the symmetric embodiments herein. Thesesymmetric embodiments still prove advantageous in terms of theirrobustness, albeit to a lesser extent than the asymmetric embodiments.

FIGS. 3A-3B illustrate additional details according to one or moresymmetric embodiments. As shown in FIG. 3A, the trip system's signalingmodule 36 includes a transmitter 90 in series with a receiver 92 betweenthe conductors 38. The arc flash protection system's signaling module 40likewise includes a transmitter 94 in series with a receiver 96 betweenthe conductors. The trip system's transmitter 90 is configured to sendthe current status signal 30 by modulating the magnitude of the currentthrough the conductors 38, while the trip system's receiver 92 isconfigured to receive the control signal 52′ by demodulating themagnitude of the current through the conductors 38, as distinctivelymodulated by the arc flash protection system's transmitter 94.Correspondingly, the arc flash protection system's transmitter 94 isconfigured to send the control signal 52 by modulating the magnitude ofthe current through the conductors 38, while the arc flash protectionsystem's receiver 96 is configured to receive the current status signal30′ by demodulating the magnitude of the current through the conductors38, as distinctively modulated by the trip system's transmitter 90.

FIG. 3B illustrates one implementation of the symmetric embodiment shownin FIG. 3A. In FIG. 3B, the trip system's transmitter 90 includes aswitched impedance element 98 that is in series with a fixed voltagesource 100. The transmitter 90 in this case is configured to modulatethe magnitude of the current through the conductors 38 by switching thetransistor associated with the switched impedance element 98, responsiveto the current status signal 30. The arc flash protection system'sreceiver 96 correspondingly includes a current sensor 102 configured tomonitor the magnitude of the current through the conductors 38 fordemodulation.

Similarly, the arc flash protection system's transmitter 94 includes aswitched impedance element 104. The transmitter 94 is configured tomodulate the magnitude of the current through the conductors 38 byswitching the transistor associated with the switched impedance element104, responsive to the control signal 52. The trip system's receiver 92correspondingly includes a current sensor 105 configured to monitor themagnitude of the current through the conductors 38 for demodulation.

In at least some embodiments, the trip system's receiver 92 isconfigured to distinguish modulation of the current by the arc flashprotection system's transmitter 94 from modulation of the magnitude ofthe current by the trip system's own transmitter 90, based on a state orchange in state of the current status signal 30. As shown, for example,the receiver 92 includes one or more receiver processing circuits 106configured to receive the current status signal 30 from the statuscircuit 28 and to identify current magnitude modulations imposed by thearc flash protection system's transmitter 94 as a function of thatsignal 30. The arc flash protection system's receiver 96 similarlyincludes one or more receiver processing circuits 108 configured toreceive the control signal 52 and to identify current magnitudemodulations imposed by the trip system's transmitter 90 as a function ofthat signal 52.

Those skilled in the art will appreciate that the signaling modules 36,40 herein are effectively interchangeable between the trip system 24 andthe arc flash protection system 26. In some embodiments, for example,the trip system's signaling module 36 sends the current status signal 30in the same way that the flash protection system's signaling module 40was described above as sending the control signal 52. Likewise, theflash protection system's signaling module 40 sends the control signal52 in the same way that the trip system's signaling module 36 wasdescribed above as sending the current status signal 52.

Those skilled in the art should appreciate that, while the Figuresillustrated the status circuits 28, 44 as being implemented within thetrip system 24 and the arc flash protection system 26 outside of therespective signaling modules 36, 40, the status circuits 28, 44 mayalternatively be implemented within those signaling modules 36, 40.

Those skilled in the art will also appreciate that, although the Figuresillustrate the trip system 24 and arc flash protection system 26 inisolation, embodiments herein extend to scenarios where at least one ofthe systems 24, 26 is interconnected to one or more other trip systemsand/or one or more other arc flash protection systems. For example,multiple trip systems may be connected in series between pairedconductors for controlling the tripping of different circuit breakersaccording to different control signals received from the arc flashprotection systems. Appropriate selection of individual voltagemagnitude ranges for the different trip systems 24 would allow the arcflash protection system 26 to uniquely distinguish different currentstatus signals received from the different systems 24. Similarly,multiple arc flash protection systems 26 may be connected to the sametrip system 24 by different pairs of conductors 38. Appropriateselection of individual current magnitude ranges for different arc flashprotection systems 26 would allow the trip system 24 to uniquelydistinguish different control signals received from the differentsystems 26. Of course, various combinations of these embodiments arealso envisioned herein.

Those skilled in the art will further appreciate that the pair ofconductors 38 herein may consist of any type of conductors. In oneembodiment, though, the conductors 38 comprise a twisted pair of wires.In other embodiments, the conductors 38 comprise a coaxial cable.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

What is claimed is:
 1. A power protection and distribution assemblycomprising an arc flash protection system configured to control a tripsystem to conditionally trip an upstream circuit breaker to isolate apower distribution bus or one of its component parts from a powersource, wherein the arc flash protection system comprises: a statuscircuit configured to generate a light status signal indicating whetheror not light characteristic of an arc event is detected; a full-duplexsignaling module comprising a transmitter in series with a receiverbetween a pair of conductors, wherein the pair of conductors couples thearc flash protection system to the trip system, wherein the receiver isconfigured to receive a current status signal from the trip system bydemodulating the magnitude of a current through the pair of conductors,the current status signal indicating whether or not currentcharacteristic of an arc event is detected by the trip system; and acontroller configured to generate, based on the light status signal andthe current status signal, a control signal for controlling the tripsystem; wherein the transmitter of the full-duplex signaling module isconfigured to send the control signal to the trip system bydistinctively modulating the magnitude of a voltage across the pair ofconductors.
 2. The power protection and distribution assembly of claim1, wherein the transmitter comprises an adjustable voltage source and isconfigured to modulate the magnitude of the voltage across the pair ofconductors by adjusting a voltage output of the adjustable voltagesource.
 3. The power protection and distribution assembly of claim 1,wherein the transmitter comprises an impedance circuit, and wherein thetransmitter is configured to modulate the magnitude of the voltageacross the pair of conductors by adjusting the impedance of theimpedance circuit.
 4. A power protection and distribution assemblycomprising an arc flash protection system configured to control a tripsystem to conditionally trip an upstream circuit breaker to isolate apower distribution bus or one of its component parts from a powersource, wherein the arc flash protection system comprises a statuscircuit configured to generate a light status signal indicating whetheror not light characteristic of an arc event is detected; a full-duplexsignaling module comprising a transmitter in parallel with a receiverand a pair of conductors, wherein the pair of conductors couples the arcflash protection system to the trip system, and wherein the receiver isconfigured to receive a current status signal from the trip system bydemodulating the magnitude of the voltage across the pair of conductors,the current status signal indicating whether or not currentcharacteristic of an arc event is detected by the trip system; and acontroller configured to generate, based on the light status signal andthe current status signal, a control signal for controlling the tripsystem; wherein the transmitter of the full-duplex signaling module isconfigured to send the control signal to the trip system bydistinctively modulating the magnitude of a current through the pair ofconductors.
 5. The power protection and distribution assembly of claim4, wherein the transmitter comprises an adjustable impedance circuit andis configured to modulate the magnitude of the current through the pairof conductors by adjusting the impedance of the adjustable impedancecircuit.
 6. The power protection and distribution assembly of claim 5,wherein the adjustable impedance circuit is configured to automaticallyself-adjust its impedance in order to substantially counteract anymodulation of the magnitude of the current through the pair ofconductors attributable to modulation by trip system of the magnitude ofthe voltage across the pair of conductors.